1. Field of the Invention
This invention relates to a camera rangefinder and, more particularly, to an active type rangefinder usable with a camera equipped with an auto-focus (AF) device, the active type rangefinder comprises a light-emitting unit and a light-receiving unit and measures a distance in the manner that ray of light is emitted by the light-emitting unit and the ray of light reflected from a subject are received by the light-receiivng unit.
2. Description of the Prior Art
Various active type rangefinders have so far been used with cameras. FIG. 1 illustrates the concept of the active type rangefinders. In the drawing, AF camera 1 is equipped with taking-lens 2, light-emitting unit 3 for measuring a distance and light-receiving unit 4 for the same. Infrared beams are emitted pulsewise from light-emitting unit 3 and are then made parallel to each other through lens 31 disposed in front of light-emitting unit 3 so as to emit in the direction intersecting them with the optical axis of camera 1 at a predetermined distance ahead from camera 1.
FIG. 2 is a circuit diagram of light-emitting unit 3. In the drawing, light-emitting element, IR-LED, is a light-emitting diode emitting infrared beams and is regulated by transistor Tr.sub.1 so as to emit infrared beams upon charging capacitor C.sub.1 for light-emitting.
The infrared beams emitted from light-emitting unit 3 hit a subject and reflect therefrom. Light-receiving unit 4 is provided with condensing lens 41 in the front thereof and light-receiving element 42 at the focal point behind condensing lens 41, respectively. The reflected beams from subject Sa at a short-distance form an optical image centering at Pa on light-receiving element 42, and the reflected beams from subject Sb at a long-distance form an optical image centering at Pb on light-receiving element 42 as well. There have been used light-receiving elements 42 such as a position sensitive detecting element, PSD, and the like by which an electric signal is generated corresponding to the position of an optical image luminance center. Distance has been measured by the electric signals generated by light-receiving element 42.